Although the low loss of optical fiber allows signals to travel hundreds of kilometers or miles, long haul lines require regenerators or repeaters to amplify the signal periodically. In the beginning, repeaters basically did comprise a receiver followed by a transmitter. The incoming signal was converted from a light signal to an electrical signal by a receiver cleaned up to remove as much signal noise as possible and then retransmitted by another laser transmitter. However, these conventional repeaters add noise to the signal and consume much power. Other disadvantages of these conventional repeaters are their complexity and inflexibility.
Consequently the electronic repeaters have been widely replaced by optical amplifiers comprising doped optical fibers.
FIG. 1 shows schematically an optical amplifier. The optical amplifier comprises a doped optical fiber dOF between a coupler and a filter. A pump laser supplies energy to the amplifier while an incoming signal stimulates emission as a pulse passes through the doped optical fiber dOF. A stimulated emission is a rapid exponential growth of photons in the doped optical fiber. The doped optical fiber dOF then can be arranged in a fiber spool. In a conventional optical amplifier, a doped optical fiber dOF with a predetermined length can be wound around a fiber spool. In order to improve a gain flatness of the optical amplifier the temperature of the optical fiber can be increased by means of a coil heater. If the coil heater is powered up the produced heat can be transferred to the fiber spool and hence to the doped optical fibers of the optical amplifier. However, such a conventional arrangement has the disadvantage that it does not provide for a uniform heating of the individual optical fiber windings wound around the fiber spool. As a consequence, the doped optical fiber wound around the spool cannot be heated accurately and the gain flatness of the optical amplifier is diminished.
Accordingly, there is a need for a fiber temperature control assembly which provides a uniform heating of the doped optical fiber wound around a fiber spool to improve gain flatness of the optical amplifier.